The last look at Herschel: A chapter in space exploration ends (pictures)

After doing yeoman work photographing the universe the last three years, the Herschel Space Observatory has finished the last of its helium coolant. Take a look back after the end of an era.

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Herschel: A look back

After running through the last of its helium coolant, the Herschel spacecraft has wrapped up its three-year journey imaging the universe. Let's take a look back at some of the stunning highlights of what turned out to be a very successful expedition.

W3 and a stellar nursery

After nearly four years of taking extraordinary images of the universe, the European Space Agency's Herschel space observatory has only weeks left before it exhausts its supply of liquid helium coolant. When the lights go out, ESA says that Herschel will have performed more than 22,000 hours of science observations, 10 percent more than originally planned, according to Leo Metcalfe, the science operations and mission manager for Herschel at ESA's European Space Astronomy Center in Madrid.

To mark the sunset of one of mankind's most successful space endeavors, it's worth taking a look back at some of the more spectacular images it's sent back to Earth.

In this picture, you can see an enormous star-forming cloud, known as W3. W3 is a giant molecular cloud containing a huge stellar nursery, some 6,200 light-years away in the Perseus Arm, one of our Milky Way galaxy’s main spiral arms. The Herschel space observatory focused on W3 for clues about how massive stars are born.

Spanning almost 200 light-years, W3 is one of the largest star-formation complexes in the outer Milky Way, hosting the formation of both low- and high-mass stars. The distinction is drawn at eight times the mass of our own sun; above this limit, stars end their lives as supernovas.

Dense, bright blue knots of hot dust marking massive star formation dominate the upper left of the image in the two youngest regions in the scene: W3 Main and W3 (OH). Intense radiation streaming away from the stellar infants heats up the surrounding dust and gas, making it shine brightly in Herschel’s infrared-sensitive eyes.

Where no telescope has gone before

Herschel launched into space on May 14, 2009, with the biggest and most powerful infrared telescope ever flown in space. The craft's main mirror measures 3.5 meters in diameter, which allowed scientists back home to study previously invisible regions as Herschel was able to record the entire wavelength spectrum from the far-infrared to sub-millimeter range.

The Andromeda galaxy

Here's an amazing shot of the Andromeda galaxy -- the nearest major galaxy to our own Milky Way, with hundreds of billions of stars -- in fine detail, as viewed by the Herschel space observatory. The red color in the image points to some of the coldest dust in the galaxy -- a few tens of degrees above absolute zero. The warmer stars are in blue.

The dark hole that is NGC 1999

Astronomers studying this infrared image believe that the dark hole -- called NGC 1999 -- seen in the green cloud at the top of this image contains fledgling stars. One of the stars is thought to be heating up the surrounding space dust and creating the bright greenish glow. The red in this image is a cloud of cold, dense gas and dust -- which forms the embryonic raw material that is the stuff of new star formation.

Hi-GAL

How much dust exists in our galaxy? That question -- one of many -- may finally get answered by a galaxy survey of infrared wavelengths officially known as the Herschel infrared Galactic Plane Survey, or Hi-GAL.

The Vela Molecular Ridge

Astronomers got a detailed look at gas and dust in this star-forming region of our Milky Way called the Vela Molecular Ridge, some 2,300 light-years away from Earth. The first stars formed here less than a million years ago.

The Southern Cross

Until Herschel came along, scientists viewing this part of the galaxy through ordinary telescopes only saw black. This region, located thousands of light-years from Earth, is called the Southern Cross, part of the constellation Crux. If your eye could make out infrared light, this spectacular image is what you'd see. Astronomers monitoring the turbulence in the region believe it is a sign that much hidden activity is taking place within these dust clouds.

A star -- many stars, actually -- is born

Star formation is on display in this whirlpool galaxy, known to astronomers as M51, some 23 million light-years away in the constellation Canes Venatici. The galaxy actually made its appearance in the annals in 1773 when it got cataloged by Charles Messier. But Messier, working with a relatively underpowered telescope, could make out very little of the whirlpool. Astronomers got their first idea of the spiral shape in 1845 using a 72-inch mirror telescope at Birr Castle, Ireland.

Crab Nebula

About six and a half thousand light-years from Earth, the Crab Nebula is all that's left from a supernova explosion witnessed by Chinese astronomers in 1054 A.D. Scientists believe this star once was as much as 15 times more massive than our own sun. What's left now is a rapidly rotating neutron star and filaments of cosmic dust -- enough dust, in fact, to make as many as 40,000 planet Earths, according to ESA.